The sophistication of unmanned air vehicles (UAVs) ranges from simple almost model aircraft like UAVs to highly sophisticated UAVs equipped with on-board instrumentation such as an altimeter, up to three gyroscopes, up to three accelerometers, and the like. Irrespective of its sophistication, control over a UAV's primary flight controls, namely, its elevators, flaps, ailerons, rudder and throttle is by means of radio signals.
Initial control over a UAV is in the hands of a control station operator. For landing a UAV, control thereover is transferred to a ground operator who is typically situated adjacent to the runway on which the UAV is to be landed. Transfer of control over the UAV occurs when it can be seen by the ground operator, it has an air speed of about 40-60 knots and a "sink rate" of about 2.2 ms.sup.-1 and it is located at a distance of between about 600 m and about 1000 m from the runway's front edge and at an altitude between about 50 m and about 100 m.
At the ground operator's disposal is a control box similar to a model aircraft's control box in that it has a left stick for respectively controlling a UAV's throttle and rudder by up/down and left/right movements and a right stick for respectively controlling its elevators and ailerons by up/down and left/right movements. In addition, the control box has a four position switch for controlling the position of a UAV's flaps.
On transfer of control, the ground operator sets the four position switch to a landing position and then relies on his judgement and intuition to handle a UAV by means of the two control sticks to land it safely on the runway. In case a ground operator senses that he cannot land a UAV safely, he aborts a landing attempt. It is well known that even a proficient ground operator can often require several attempts to land a UAV safely due to lack of the "feel" of the UAV's responses to his commands, the affects of wind gusts, and the like.
In GB-A-2 224 613, there is described an automatic aircraft landing system and a corresponding method for automatically landing an aircraft on a runway. The system includes data acquisition apparatus for acquiring flight data pertaining to the descent of an aircraft on a flight path defined between a final capture point and a touchdown point on a runway and a controller responsive to the flight data for providing control signals to at least one of the aircraft's primary controls for urging the aircraft to essentially adhere to a guide path along at least an upper portion of its flight path.
In Patent Abstracts of Japan, vol. 17, no. 330 (M-1434), 23.06.93 and JP-A-05 039094, 19.02.93, there is described a fuzzy logic based landing control device for automatically landing a helicopter after its engine is stopped in flight and the helicopter is in its autorotation state.